This invention relates to a developer collection system comprising a plurality of image carrier members, a plurality of developing apparatus for developing the electrostatic latent images formed on the plurality of image carrier members by means of liquid developers carried by non-volatile respective solvents, an intermediate transfer member for sequentially transferring the toner images developed by the primary transfer sections respectively corresponding to the plurality of image carrier members, superposing them one on the other to form a developer image and carrying and conveying the developer image and an output apparatus for transferring the developer image from the intermediate transfer member on a sheet on a sheet conveyance route in a secondary transfer section for output, and adapted to collect the excessive developers from the plurality of image carrier members, the plurality of developing apparatus, the intermediate transfer member and the output apparatus. The present invention also relates to an image forming apparatus adapted to transfer a toner image formed by laying one on the other from the intermediate transfer member on a sheet in a secondary transfer section and output the image.
Various wet type image forming apparatus for developing a latent image by means of a highly viscose liquid developer prepared by dispersing solid toner into a liquid solvent and visualizing the electrostatic latent image have been proposed. A developer to be used in such wet type image forming apparatus is prepared by suspending solid (toner particles) in an electrically insulating organic solvent (carrier), which is typically made of silicon oil, mineral oil or edible oil. Toner particles are very fine and have a particle diameter of about 1 μm. Thus, if compared with dry type image forming apparatus adapted to use powdery toner particles having a particle diameter of about 7 μm, wet type image forming apparatus can produce high quality images because they use such fine toner particles.
The carrier of a developer operates to prevent fine toner particles with a diameter of about 1 μm from flying away, hold toner particles in an electrically charged state and uniformly disperse them. It also operates to make toner particles easily move under the effect of an electric field in the development step and the transfer step. Thus, while the carrier is an element necessary for storing and transporting toner and also in the development step and the transfer step, it can adhere to non-image regions and, after developing a latent image, the excessive carrier can give rise to a problem of disturbed image transfer and other problems. To avoid these problems, the carrier is removed (squeezed) from the developer on the photosensitive member and the intermediate transfer member as ordinary practice (see, inter alia, Patent Document 1: Jpn. Pat. Appln. Laid-Open Publication No. 2002-296918). When an intermediate transfer belt and a secondary transfer belt are used in wet type image forming apparatus, the liquid developer (including the carrier and the solid) adhering to the surfaces of the belts is removed by means of a cleaning blade (see, inter alia, Patent Document 2: Jpn. Pat. Appln. Laid-Open Publication No. 2002-189354). In the developer recycling process, a plurality of developing apparatus are arranged selectively vis-à-vis the photosensitive drum and squeezing apparatus are arranged also selectively vis-à-vis the photosensitive drum at the downstream side of the developing apparatus to correspond to the latter in order to squeeze the excessive developers on the photosensitive drum by means of the squeezing apparatus and circulate and transport the excessive developers collected by the squeezing apparatus to the developing apparatus by means of a circulating apparatus for the purpose of recycling (see, inter alia, Patent Document 3: Jpn. Pat. Appln. Laid-Open Publication No. 2003-107913).